Davey Gravey this is an unusual error for a main board but it is possible. This "but I'm having trouble finding one." is a pretty good indication, that this particular TV has main board issues. The reason for you not finding is, could be that others needed those as well and bought whatever they could. Then there is a possibility that the manufacturer just stopped building them, because of design errors etc. There are places that may repair your main board instead of replacing it. Take some good pictures of the main board and post those with your QUESTION as well.
It is possible that this is not a main board fault but actually a panel issue. However, there is no information about the panel available. See if you can get a replacement main board relatively inexpensive and that you can return it, if this does not resolve the issue.